1. Field of the Invention
The present invention relates to a VVA (valley vertical align)-mode liquid crystal display (LCD), and more particularly to a VVA-mode LCD having improved transmittance and response speed.
2. Description of the Prior Art
LCDs have been developed to replace CRTs. In particular, TFT LCDs have a colorful display screen of excellent quality and large size, comparable to that of CRTs, and are highly visible in the laptop computer, PC, and monitor markets. Furthermore, they are expected to encroach on the TV market.
In general, LCDs using vertical alignment distort the electrical field applied to upper and lower substrates to align liquid crystals in two or four directions for an improved viewing angle. In VVA-mode LCDs, a pinwheel structure is currently proposed wherein the electrical field is distorted in a circular shape to drive liquid crystals in a pinwheel configuration to improve the viewing angle. Instead of placing protrusions or slits on the upper substrate as a tilting source, valleys are formed as a tilting source to lay the liquid crystals in a pinwheel configuration for an improved viewing angle.
In addition, a process for forming circular grooves on the upper or lower substrate to form valleys is performed, instead of a process for forming protrusions on the upper substrate, to form color filters on the upper substrate together with valleys. This simplifies the process and reduces transmittance loss by forming disclination lines at the center of the valleys.
A conventional VVA-mode LCD will now be described.
Although not shown, a lower substrate and an upper substrate having a pixel electrode and a counter electrode, respectively, are bonded to each together with a liquid crystal layer having negative anisotropy of dielectric constant interposed between them. Vertical alignment layers are interposed between the lower substrate and the liquid crystal layer and between the upper substrate and the liquid crystal layer, respectively. Polarization plates are attached to the rear surfaces of the facing surfaces of the substrates, respectively, in such a manner that their polarization axes cross each other.
Color resin layers of red (R), green (G), and blue (B) are interposed between the upper substrate and the counter electrode to implement respective colors. The color resin layers have a number of (e.g., 2–10) valleys regularly formed thereon in each portion corresponding to a pixel.
However, disclination lines A inevitably occur about the valleys 3, as shown in FIG. 1A. This reduces transmittance and degrades response characteristics. Reference numeral 1 refers to a pixel electrode, 2 is a slit pattern, and 4 is a liquid crystal.
A number of valleys 3 formed at the center of the upper substrate, as shown in FIG. 1B, provide a tilting source. This results in losses of transmittance and color characteristics. Reference numeral 6 refers to a data line, 7 is a gate line, and 8 is a TFT. In particular, the distance between the valleys and the slits affects driving stability and response speed and, if the distance increases, they degrade. The size of the valleys must increase, therefore, for improved driving stability and response speed. However, this deteriorates color reproduction property.